This invention relates to a digital image recording and/or reproduction method and an apparatus by which a digital image signal is coded and recorded on a recording medium and/or read and decoded for reproduction.
On a software tape for use with an analog video tape recorder, a signal is recorded so as to disturb operation of an AGC (Automatic Gain Control) of a recording amplifier of a video tape recorder. The disturbing signal is inserted in a predetermined line within a vertical blanking period of a television signal for the object of copyright protection. Due to this disturbing signal, when a software tape is illegally dubbed, then the dubbed tape is recorded in a condition wherein the reproduced signal is illegible. As a result, the copyright is protected.
On the other hand, in digital video tape recorders, an image compression technique has made a remarkable development in recent years. It is a common practice to decrease the overall amount of recording signals in order to improve the picture quality. Therefore, such portions as a vertical blanking portion are omitted, because they have no direct relationship to the picture.
For example, in the case of the 525/60 system, 720 samples of data for an effective scanning period shown in FIG. 39 are extracted with respect to 240 lines out of 23H to 262H in an odd-numbered field and 240 lines out of 285H to 524H in an even-numbered field. Similarly, in the case of the 625/50 system, 720 samples of data for an effective scanning period shown in FIG. 39 are extracted with respect to 288 lines out of 23H to 310H in an odd-numbered field and 288 lines of 335H to 622H in an even-numbered field.
Image data obtained by extracting only actual image portions in this manner are compressed to reduce the amount of data recorded. Thus recorded image data are processed, upon reproduction, by reverse processes to those performed upon recording.. Therefore, the vertical blanking portions and horizontal blanking portions, which were deleted upon recording, are added to the image data so that a composite video signal are outputted.
When it is tried to make a software tape for a digital video tape recorder using such an image compression technique as described above, since only actual image portions are recorded as described above, it is impossible to insert a disturbing signal for a vertical blanking period, which is recorded inserted in a software tape for use with an analog VTR for the object of copyright protection.
The SCMS (Serial Copy Management System) which has been put into practical use in the field of digital audio tapes is effective for the copyright protection between digital video tape recorders. It cannot be anticipated for digital video tape recorders the same kind of copyright protection which is adopted in analog video tape recorders such as VHS video tape recorders, most popularly spread at present.